When upgrading the test data twice, don't bail out because of an existing backup

BUG=none
R=jkummerow@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/183853004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19605 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Update test262 to get test data from github

BUG=none
R=jkummerow@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/184223002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19606 ce2b1a6d-e550-0410-aec6-3dcde31c8c00